<h1 id="michigan-congressional-districts">2020 Michigan Congressional
Districts</h1>
<h2 id="redistricting-requirements">Redistricting requirements</h2>
<p>In Michigan, districts must:</p>
<ol type="1">
<li>be contiguous (Mich. Const. art. IV, § 6(13)(b)). Island areas are
considered to be contiguous by land to the county of which they are a
part.</li>
<li>have equal populations (Mich. Const. art. IV, § 6(13)(a))</li>
<li>be geographically compact (Mich. Const. art. IV, § 6(13)(g))</li>
<li>reflect consideration of county, city, and township boundaries
(Mich. Const. art. IV, § 6(13)(f))</li>
<li>not provide a disproportionate advantage to any political party,
determined using accepted measures of partisan fairness (Mich. Const.
art. IV, § 6(13)(d))</li>
</ol>
<p>Based on the current plan, two districts should be majority-minority
in order to comply with the Voting Rights Act.</p>
<h3 id="algorithmic-constraints">Algorithmic Constraints</h3>
<p>We enforce a maximum population deviation of 0.5%. We apply a
county/municipality constraint, as described below. We target a 52-62%
minority share in two districts.</p>
<h2 id="data-sources">Data Sources</h2>
<p>Data for Michigan comes from the ALARM Project’s <a
href="https://alarm-redist.github.io/posts/2021-08-10-census-2020/">2020
Redistricting Data Files</a>.</p>
<h2 id="pre-processing-notes">Pre-processing Notes</h2>
<p>To meet contiguity requirements, we removed precincts with more water
area than land area and no population. We then manually connected any
disconnected islands with the nearest precinct on the mainland and in
the same county: precincts 26029029017 and 26029029016 in Charlevoix
county, and precincts 26047047022 and 26097097010 for the Upper
Peninsula.</p>
<h2 id="simulation-notes">Simulation Notes</h2>
<p>We sample 48,000 districting plans for Michigan across four
independent runs of the SMC algorithm, then filter down to 5,000 total
plans. To balance county and municipality splits, we create
pseudocounties for use in the county constraint. These are counties,
outside of Wayne, Macomb, and Oakland counties. Within these counties,
municipalities are each their own pseudocounty as well. These counties
were chosen since they are necessarily split by congressional districts.
Overall, this approach leads to much fewer county and municipality
splits than using either a county or county/municipality constraint.</p>
<h2 id="contents">Contents</h2>
<ul>
<li><code>MI_cd_2020_stats.csv</code> contains summary statistics on the
sampled redistricting plans</li>
<li><code>MI_cd_2020_plans.rds</code> is a compressed
<code>redist_plans</code> object, which contains the matrix of
precinct/block assignments and may be used for further analysis.</li>
<li><code>MI_cd_2020_map.rds</code> is a compressed
<code>redist_map</code> object, which contains the precinct/block
shapefile and demographic data.</li>
</ul>
<p>Both the <code>redist_plans</code> and <code>redist_map</code> object
are intended to be used with the <a
href="https://alarm-redist.github.io/redist/">redist package</a>.</p>
<h3 id="codebook-for-summary-statistics">Codebook for summary
statistics</h3>
<ul>
<li><code>draw</code>: unique identifier for each sample. Non-numeric
draw names are real-world plans, e.g., <code>cd_2010</code> for an
enacted 2010 plan.</li>
<li><code>district</code>: a district identifier. District numbers
roughly match those in the enacted plan, but the correspondence is not
perfect.</li>
<li><code>chain</code>: a number identifying the run of the
redistricting algorithm used to produce this draw. Used for diagnostic
purposes.</li>
<li><code>pop_overlap</code>: a number indicating the fraction of people
in this plan who reside in the same-numbered district in the enacted
plan.</li>
<li><code>total_pop</code>: the total population of each district.</li>
<li><code>total_vap</code>: the total voting-aged population of each
district.</li>
<li><code>pop_*</code>, <code>vap_*</code>: total (voting-aged)
population within racial and ethnic groups for each district. Variable
codes documented <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>plan_dev</code>: the maximum population deviation among
districts in the plan. Computed as
<code>max(abs(distr_pop - target_pop)/target_pop)</code>.</li>
<li><code>comp_edge</code>: compactness, as measured by the fraction of
internal edges kept. Higher values indicate more compactness.</li>
<li><code>comp_polsby</code>: compactness, as measured by the
Polsby-Popper score. Higher values indicate more compactness.</li>
<li><code>county_splits</code>: the number of counties which belong to
more than one district.</li>
<li><code>muni_splits</code>: the number of Census Designated Places
which belong to more than one district.</li>
<li><code>*_##_dem_*</code>, <code>*_##_rep_*</code>: vote counts for
statewide Democratic and Republican candidates in a certain election.
More information <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>adv_##</code>, <code>arv_##</code>: average vote counts for
statewide Democratic and Republican candidates in a certain year. More
information <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>ndv</code>, <code>nrv</code>: averages of the
<code>adv_##</code> and <code>arv_##</code> variables across all
available elections.</li>
<li><code>ndshare</code>: normal Democratic share, computed as
<code>ndv / (ndv + nrv)</code></li>
<li><code>e_dvs</code>: average Democratic vote share, computed as the
average of the Democratic vote share when first scored under each
statewide election.</li>
<li><code>pr_dem</code>: probability seat is represented by a Democrat;
calculated as the fraction of statewide elections under which the
district had a majority Democratic share.</li>
<li><code>e_dem</code>: expected number of Democratic seats for the
plan; equivalent to summing the <code>pr_dem</code> values across
districts</li>
<li><code>pbias</code>: partisan bias at 50% vote share, averaged across
all available elections. Positive values indicate Republican bias.</li>
<li><code>egap</code>: the efficiency gap, averaged across all available
elections. Positive values indicate Republican bias.</li>
</ul>
